The overall project seeks an understanding in detail of the kinetic, chemical, and complete metal ion dependent stereochemical mechanisms utilized by the first enzyme of histidine biosynthesis in Salmonella typhimurium ATP phosphoribosyltransferase (EC 2.4.2.17) to effect integrated metabolic regulation. We are studying the kinetics of the modification with pyridoxal phosphate, dial AMP, butane dione, and phenylglyoxal of lysine and arginine residues at the active site of the enzyme. We also will conduct ppGpp kinetics of inhibition studies in an effort to decide whether this regulatory ligand acts at the active site or at an allosteric site. Binding studies on the enzyme substrates will be pursued to provide more information regarding the order of substrate binding. We hope to substantially finish the chemical definition of the active site structure and its course ligand binding properties.